The NAC genes (including NAM, ATAF1, ATAF2 and CUC2) belong to a relatively large gene family found only in plants thus far. These genes encode proteins which are conserved in their N-terminal ˜170 amino acids but are highly divergent in their C-termini. Previous genetic studies in petunia (Souer et al., 1996) and Arabidopsis (Aida et al., 1997) have suggested that some members of the NAC family play a role in patterning of the shoot and floral meristem.
Petunia embryos carrying the no apical meristem (nam) mutation fail to develop a shoot apical meristem. Occasional shoots on nam seedlings bear flowers that develop ten instead of five primordia in the second whorl. Double mutants with the homeotic gene green petals show that nam acts independently of organ identity in whorl 2 and also affects primordium number in whorl 3. Strikingly, nam mRNA accumulates in cells at the boundaries of meristems and primordia. It has been shown that nam plays a role in determining positions of meristems and primordia (Souer et al., 1996).
Mutations in CUC1 and CUC2 (for CUP-SHAPED COTYLEDON), which are genes of Arabidopsis, cause defects in the separation of cotyledons (embryonic organs), sepals, and stamens (floral organs) as well as in the formation of shoot apical meristems. These defects are most apparent in the double mutant. Phenotypes of the mutants suggest a common mechanism for separating adjacent organs within the same whorl in both embryos and flowers. The CUC2 gene was cloned and found to encode a protein homologous to the petunia NAM protein (Aida et al., 1997).
The publications and other materials used herein to illuminate the background of the invention or provide additional details respecting the practice, are incorporated by reference, and for convenience are respectively grouped in the appended List of References.